Graptolite-derived organic matter in the Wufeng–Longmaxi Formations (Upper Ordovician–Lower Silurian) of southeastern Chongqing, China: Implications for gas shale evaluation

Luo, Qingyong; Zhong, Ningning; Dai, Na; Zhang, Wang

doi:10.1016/j.coal.2015.11.014

Cited by 142 publications

(60 citation statements)

References 35 publications

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“…The results show that the C content in graptolites is very high, and it was inferred that graptolites were the dominant contribution to the organic component (Figure a,b). This finding is in agreement with the results of Petersen, Schovsbo, and Nielsen () and Luo, Zhong, Dai, and Zhang ().…”

Section: Discussionsupporting

confidence: 93%

Comparative study of nanoscale pore structure of Lower Palaeozoic marine shales in the Middle‐Upper Yangtze area, China: Implications for gas production potential

et al. 2017

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The Lower Cambrian Niutitang and Lower Silurian Longmaxi shales in the Middle‐Upper Yangtze area are considered the primary shale gas units targeted for development in China. To shed some light on the difference in nanopore structures between Niutitang and Longmaxi shales, systematic comparative investigations were conducted using various techniques, including geochemical analyses, field emission scanning electron microscopy (FE‐SEM), high‐pressure mercury intrusion porosimetry (MIP), and low‐pressure N2/CO2 adsorption techniques. The results show that both Niutitang and Longmaxi shales have high total organic carbon (TOC) content and complex mineral compositions. The porosity of Longmaxi shales is higher than that of Niutitang shales, with an average value of 3.26% and 2.04%, respectively. Interestingly, for both shale formations, the mesopores (2–50 nm) are the major contributors to pore volumes, whereas the specific surface area is dominated by micropores (<2 nm). For the mesopore size distributions (PSDs) calculated from the N2 adsorption, the Longmaxi shales have a dominant pore size ranging from 10 to 60 nm. In contrast, there are more fine mesopores (2–8 nm) in the Niutitang shales. Furthermore, we found that numerous nanoscale pores are well‐developed within graptolite‐derived organic matter (OM) in the Longmaxi shales. These interconnected graptolite periderm pore systems may not only provide a storage space for both adsorbed and free gas but also serve as pathways for gas transport. The Niutitang shales developed relatively fewer OM pores with smaller diameters, lower OM surface porosity, and lower connectivity compared to the Longmaxi shales. The differences in OM pore structure partly explain why there is a large production difference between these two formations.

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Section: Discussionsupporting

confidence: 93%

Comparative study of nanoscale pore structure of Lower Palaeozoic marine shales in the Middle‐Upper Yangtze area, China: Implications for gas production potential

et al. 2017

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“…The knowledge of effective mineralogy complicated the influence of clay minerals on the pore structure. The biogenic quartz produced by precipitation during diagenesis with silica is derived from graptolite and radiolarians [57], which may also control the pore volume and structure in shales. This type of quartz affects microporosity significantly and has certain correlation to TOC content.…”

Section: Evolution Of Pore Structure In the Shale Of Detachment Layersmentioning

confidence: 99%

A Discussion on the Detachment Structural Deformation and Its Influence on Pore Structure Evolution in Shale on the Western of the Xuefeng Mountain, South China

Liang¹,

Wang²,

Zhang³

et al. 2018

Tectonics - Problems of Regional Settings

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Detachment structures occur widely in the crust, and it is the commonest and most important deformation type developed in the region between orogenic belts and basins. Organic-rich shale, as the weak layers, usually acts as slippery layers in detachment structural deformation systems. The "comb-like" and "tough-like" fold belts on the western side of the Xuefeng Mountain result from the multilayer detachment, and their formation is different from the typical Jura type structures. The reason is that there are several detachment layers and detachment systems in the stratigraphic column from the Neoproterozoic upwards to the Mesozoic in the study area. As the stress decoupling role, the shale slippery layers tend to undergo strong deformation in the detachment systems and impacted on pore structure evolution in the shale. In order to obtain the detachment structural deformation and its influence on pore structure evolution in shale on the Middle and Upper Yangtze, the structural and textural, geochemical and mineralogical properties analysis, porosity and pore structure feature investigations are performed using shale samples collected from the same shale bed of the Longmaxi Formations (Lower Silurian) of Western of the Xuefeng Mountain, South China.

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“…The thin section analysis reveals grainstones (Yijianfang Fm) as being the dominant rock type including fine‐grained intraclasts and bioclasts cemented by calcite (Figure a–c). The intraclasts are mainly composed of reworked limestone debris, and bioclasts are mainly fossils of small shells and graptolites (Luo, Zhong, Dai, & Zhang, ) replaced by calcite (Figure a–c). In addition, cracks are widely developed in the samples, and conjugate cracks are occasionally observed under the microscope (Figure b).…”

Section: Fluid Inclusions Researchmentioning

confidence: 99%

Natural gas characteristics, fluid evolution, and gas charging time of the Ordovician reservoirs in the Shuntuoguole region, Tarim Basin, NW China

Wang

et al. 2017

Geological Journal

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The Shuntuoguole region is situated at the center of the Tarim Basin, in NW China. It is bordered by the Tazhong Uplift to the west and the Manjiaer Depression to the east. Data obtained on samples collected from exploration wells highlight the large potential for gas discoveries in this region. Component and stable carbon isotopic analyses have been performed on gas samples from 5 wells in the Shuntuoguole region. The dryness coefficients of gas samples vary from 0.95 to 1.00, indicating that the gas samples belong to overmatured dry gas. The carbon isotopic values (δ13C) of all gas samples are heavier than −40‰, compared to the typical gas samples with different sources in the Tarim Basin, revealing that the gas in the Shuntuoguole region originated from source rocks in the Cambrian. The SN‐1 exploitation well was selected to undertake fluid inclusion studies revealing the mechanisms of natural gas charging and fluid evolution. Data from the SN‐1 well drill core indicate a 1,700‐ to 7,050‐m‐thick sedimentary sequence containing Ordovician to Tertiary strata. The Middle Ordovician Yijianfang Formation (Fm) constitutes one of the most important gas reservoirs. The Yijianfang Fm consists principally of limestone containing widely distributed sparry calcite. Numerous fluid inclusions are observed in calcite, and 4 types of fluid inclusions are recognized based on the observed phases and components. These are pure CH4 (P‐type), CH4‐bearing (C‐type), aqueous (W‐type), and solid‐bearing (S‐type) inclusions. The trapping temperatures and pressures, determined through the intersection of isochores from coeval fluid inclusions, reach 183 °C to 216 °C and 1,914 bars to 2,196 bars, respectively. When taking into account the regional burial history, we find the natural gas charged during the Neogene interval, from 20 Ma to 3 Ma.

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Graptolite-derived organic matter in the Wufeng–Longmaxi Formations (Upper Ordovician–Lower Silurian) of southeastern Chongqing, China: Implications for gas shale evaluation

Cited by 142 publications

References 35 publications

Comparative study of nanoscale pore structure of Lower Palaeozoic marine shales in the Middle‐Upper Yangtze area, China: Implications for gas production potential

Comparative study of nanoscale pore structure of Lower Palaeozoic marine shales in the Middle‐Upper Yangtze area, China: Implications for gas production potential

A Discussion on the Detachment Structural Deformation and Its Influence on Pore Structure Evolution in Shale on the Western of the Xuefeng Mountain, South China

Natural gas characteristics, fluid evolution, and gas charging time of the Ordovician reservoirs in the Shuntuoguole region, Tarim Basin, NW China

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